Metal sheet pressing method

ABSTRACT

This invention provides a metal sheet pressing method of precision-pressing a metal sheet, wherein after a metal sheet ( 1 ) is partially drawn so as to form a perforated portion ( 1   a ), the perforated portion ( 1   a ) is heated by baking and after it is heated by baking, the perforated portion ( 1   a ) is pressed with press dies into an uneven-surface shape.

This application is a continuation of U.S. application Ser. No.10/621,309, filed Jul. 18, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for pressing a steel sheet andmore particularly to improvement of a pressing method for pressing afragile portion of a steel sheet.

2. Description of Prior Art

As a conventional method for pressing a metal sheet such as steel sheet,it has been well known that a thin steel sheet is placed on dies andpressed with a punch into a product configuration.

The above-mentioned pressing method with the punch has variousinconveniences described below and therefore, means for solving theseproblems has been demanded.

That is, a formation method of pressing with the punch comprised ofsimple processes is not good at formation of a complicateduneven-surface shape. To cope with this problem, it is necessary, forexample, to retard pressing speed extremely or deepen the formationgradually through multiple pressing steps.

This problem is particularly remarkable in formation of a fragileportion in which a narrow frame or meshes are formed. In the case wheresuch a fragile portion is formed according to the formation method ofpressing with a punch, work efficiency and formation efficiency droplargely.

In the case of forming a fragile portion having the narrow frame ormeshes into an uneven-surface shape according to the method of pressingwith the punch, actually, such a form as the narrow frame, meshes ispunched out and then, a final product is drawn gradually through severalsteps using multiple dies each having a different degree of unevenness.

Even if such a press work with a great deal of labor and time isconducted, an uniform shape in that fragile portion cannot be maintainedand it is difficult to draw a target material into a correct shape witha uniform thickness. Further, because a partial fracture or the like islikely to occur, the percentage of defects and manufacturing cost areincreased.

SUMMARY OF THE INVENTION

In view of the above-described defects of the conventional method whichneeds a great deal of time and labor, an object of the present inventionis to provide a metal sheet pressing method of pressing a metal sheetinto an uneven-surface shape with press dies, in which a precisionpressing work can be done with ease. Particularly, the present inventionaims at providing a pressing method capable of pressing only a fragileportion so as to form an uneven-surface shape accurately when a metalsheet is subjected to precision-pressing work.

The metal sheet pressing method of precision-pressing the metal sheetproposed by the present invention to achieve the above-described objectwill be described with reference to the accompanying drawings. That is,after a metal sheet 1 is partially drawn so as to form a perforatedportion 1 a, the perforated portion 1 a is heated by baking and after itis heated by baking, the perforated portion 1 a is pressed with pressdies 3 a, 3 b into an uneven-surface shape.

The perforated portion 1 a of the metal sheet 1 can be formed into amesh-like shape as shown in FIG. 1.

According to the present invention, when the metal sheet 1 isprecision-pressed, only a fragile portion such as the perforated portion1 a formed by drawing is heated by baking as shown in FIG. 3. Next, asshown in FIG. 4, the fragile portion after heated by baking is pressedwith press dies 3 a, 3 b having an uneven-surface shape corresponding tothe uneven-surface shape 1 b (shown in FIG. 2) to be finally formed.Consequently, the fragile portion can be stretched uniformly and largelythrough a single process. Consequently, uneven-surface shape can beformed accurately. As a result, a metal sheet pressing method by whichuneven-surface shape can be formed accurately without any formationdefect is achieved. And, according to this method, forming speed can bereduced.

As a metal sheet to be pressed, steel sheet, stainless steel sheet andthe like can be employed. Namely, common steel, austenitic basestainless steel, ferrite base stainless steel, martensite stainlesssteel, two-phase stainless steel and the like can be employed.

According to the present invention, after the metal sheet is partiallydrawn so as to form the perforated portion, the perforated portion isheated by baking and after it is heated by baking, the perforatedportion is pressed with press dies into a desired uneven-surface shape.As a steel sheet to be adopted as that metal sheet, it is preferable touse a steel sheet whose property is not changed despite annealing andwhich exerts the same characteristic as before heating after it iscooled. The before described austenitic base stainless steel, ferritebase stainless steel, martensite stainless steel and two-phase stainlesssteel satisfy these requirements.

Heating of the perforated portion 1 a by baking can be carried out attemperatures of 800 to 1,000° C. with a heating unit such as a burner asshown in FIG. 3. At this time, preferably, the fragile portion such asthe perforated portion 1 a formed by drawing is heated accurately bybaking. Then, as a good measure for this purpose, a fence 4 is providedas shown in FIG. 3 to protect a flame of the heating unit 2 fromswinging.

As described above, according to the present invention, only the fragileportion in the metal sheet formed by drawing is heated by baking, sothat the uneven-surface shape can be formed precisely and easily bypressing. Consequently, the fragile portion in which a frame or meshesare formed by drawing can be stretched accurately into a proper shapewith a uniform thickness and formed into an uneven-surface shape of adesired size. Consequently, productivity is improved and further,percentage of defects can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view for explaining a state in which a metal sheet ispartially drawn;

FIG. 2 is a sectional view taken along the line A-A of a metal sheetpressed according to the method of the present invention;

FIG. 3 is a sectional view taken along the line A-A in FIG. 1 forexplaining heating process by baking; and

FIG. 4 is a sectional view taken along the line A-A in FIG. 1 forexplaining a process of pressing a fragile portion after the heatingprocess by baking.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiment of the present invention will bedescribed with reference to the accompanying drawings.

When an austenitic base stainless steel sheet having a thickness of 0.5t is formed by drawing into a desired product shape as shown in FIG. 1,its perforated portion 1 a is formed into meshes about 5 mm.

Only the perforated portion 1 a formed in the mesh form is heated bybaking locally to approximately 800 to 1,000° C. with a heating unit 2such as a gas burner as shown in FIG. 3.

According to the embodiment shown in FIG. 3, a fence 4 is provided toprevent a flame from the heating unit 2 from swinging so that only theperforated portion 1 a is heated accurately by baking.

After that, as shown in FIG. 4, by using pressing dies 3a, 3bcorresponding to an uneven-surface shape to be formed finally as shownin FIG. 2, the perforated portion 1 a, after heated by baking, ispressed into a protruded form having a radius of about 50 mm. Since atthis time, other portion than the perforated portion 1 a subjected toheat treatment by baking is not heated, the other portion than theperforated portion 1 a maintains its proper shape as a frame so as toform an uneven-surface shape accurately when the perforated portion 1 ais pressed.

Consequently, a product in which the perforated portion 1 a, which isthe fragile portion, is formed such that it is largely protruded can beformed as shown in FIG. 2.

In the foregoing, preferable embodiment of the present invention isdescribed, but the present invention is not limited to theabove-described embodiment and can be carried out in various modeswithin the technical scope described in the claims.

1. A metal sheet pressing method of precision-pressing a metal sheet,wherein after a metal sheet is partially drawn so as to form aperforated portion, the perforated portion is heated by baking and afterit is heated by baking, the perforated portion is pressed with pressdies into an uneven-surface shape.
 2. A metal sheet pressing methodaccording to claim 1, wherein the perforated portion of the metal sheetis formed in a mesh shape.